Hydraulic elevators utilize a piston assembly to urge a car upwardly in a hoistway. The piston assembly comprises a piston disposed within a cylinder. The piston is urged upwardly by a machine comprising a motor, a motor driven pump, and a valve assembly. To raise the car, fluid is pumped through the valve assembly into the piston assembly, causing the piston to rise. To lower the car, fluid is allowed to flow out of the piston assembly, through the valve assembly, and back to the tank.
Hydraulic machines are submerged in a reservoir or tank containing hydraulic fluid. Tanks are usually rectangularly shaped and are made out of flat sheet steel or the like.